1. Field of the Invention
The present invention relates to a photosensitive polymer and to a chemically amplified photoresist composition containing the same.
This application is a counterpart of, and claims priority to, Korean Application No. 99-31060, filed Jul. 29, 1999, the contents of which are incorporated herein by reference.
2. Description of the Related Art
As semiconductor devices become highly integrated, photolithography processes used in the fabrication of such devices must be capable of forming ultra-fine patterns. For example, a sub-quarter micron or smaller sized pattern is needed in a semiconductor memory device having a capacity exceeding 1 Gbit. As such, a photolithography technology has been proposed which employs an argon fluoride (ArF) excimer laser as a new type of light source. This is because the ArF laser exhibits a wavelength (193 nm) which is shorter than the wavelength (248 nm) of a conventional krypton fluoride KrF excimer laser. Therefore, a demand has arisen for chemically amplified photoresist polymers and photoresist compositions which are suitable for use with the ArF excimer laser.
In general, a chemically amplified photoresist composition for an ArF excimer laser should exhibit the following characteristics: (1) transparency at a wavelength of 193 nm; (2) excellent thermal properties (for example, high glass transition temperature); (3) good adhesion to underlying (and overlying) film materials; (4) high resistance to dry etching; and (5) easily capable of being developed using developing solutions which are in widespread use in the manufacture of semiconductor devices, for example, 2.38% by weight of tetramethyl ammonium hydroxide (TMAH).
However, a terpolymer comprising methylmethacrylate, t-butyl methacrylate and methacrylic acid, which is a widely known chemically amplified photoresist polymer for the ArF excimer laser, does not exhibit all of the above-mentioned characteristics. In particular, the terpolymer has a very low resistance to dry etching, a low adhesion to underlying film materials and low wettability for a developing solution.
Recently, attempts have been made to increase the etching resistance of a photosensitive polymer for the ArF excimer laser by introducing alicyclic compounds, for example, isobornyl, adamantyl or tricyclodecanyl group, into the backbone of the polymers. However, these polymers also have several disadvantages. For example, their etching resistance is still not acceptable and their adhesion characteristics to underlying films are still poor, which results in lifting of photoresist patterns.
It is an objective of the present invention to provide a photosensitive polymer which is capable of being exposed using an ArF excimer laser, and which has an improve etching resistance and an improved adhesion to an underlying film or substrate.
It is another objective of the present invention to provide a chemically amplified photoresist composition containing the photosensitive polymer.
Accordingly, to achieve the above objective, there is provided a photosensitive polymer including a first monomer which is norbornene ester having C1 to C12 aliphatic alcohol as a substituent, and a second monomer which is maleic anhydride.
Preferably, the C1 to C12 aliphatic alcohol is secondary alcohol.
The photosensitive polymer according to the present invention may further include at least one third monomer selected from the group consisting of norbornene carboxylic acid, norbornene ester having a C6 to C20 alicyclic ester having C as a substituent, norbornene ester having an acid-labile group as a substituent, (meth)acrylic acid, (meth)acrylate having C1 to C12 aliphatic alcohol as a substituent, (meth)acrylate having an acid-labile group as a substituent, and (meth)acrylate having a C6 to C20 alicyclic ester having C as a substituent.
In the case where the third monomer is norbornene ester having a C6 to C20 alicyclic ester having a C group or (meth)acrylate having a C6 to C20 alicyclic ester as a substituent, the first monomer may be norbornene having C1 to C12 aliphatic alcohol as a substituent, norbornene carboxylic acid, norbornene having C1 to C12 aliphatic ester having C group having carboxy group pendent thereto as a substituent, or norbornene having C1 to C12 aliphatic ester having a C group having a carboxylic anhydride group pendent thereto as a substituent.
According to another aspect of the present invention, there is provided a photosensitive polymer including, in addition to the first and second monomers, a third monomer selected from the group consisting of norbornene carboxylic acid, norbornene ester having C6 to C20 aliphatic ester having a C group as a substituent and norbornene ester having an acid-labile group as a substituent, and a fourth monomer selected from the group consisting of (meth)acrylic acid, (meth)acrylate having C1 to C12 aliphatic alcohol as a substituent, (meth)acrylate having an acid-labile group as a substituent and(meth)acrylate having an aliphatic ester having a C group as a substituent.
In the case where the third monomer is (meth)acrylate having C6 to C20 alicyclic ester having a C group as a substituent, the first monomer may be norbornene having C1 to C12 aliphatic alcohol as a substituent, norbornene carboxylic acid, norbornene having C1 to C12 aliphatic ester having a C group having carboxy group pendent thereto as a substituent, norbornene having C1 to C12 aliphatic ester having a C group having a carboxylic anhydride group pendent thereto as a substituent, and norbornene ester having C1 to C12 aliphatic alcohol having a carboxylic anhydride group pendent thereto as a substituent.
Also, the present invention provides photosensitive polymer including a first monomer selected from the group consisting of norbornene having C1 to C12 aliphatic alcohol as a substituent, norbornene carboxylic acid, norbornene having C1 to C12 aliphatic ester having a C group having carboxy group pendent thereto as a substituent, norbornene having C1 to C12 aliphatic ester having a C group having a carboxylic anhydride group pendent thereto as a substituent, and norbornene ester having C1 to C12 aliphatic alcohol having a carboxylic anhydride group pendent thereto as a substituent, a second monomer which is maleic anhydride, a third monomer which is norbornene ester having an acid-labile group as a substituent, and a fourth monomer which is norbornene ester having C6 to C20 alicyclic ester having a C group as a substituent.
To accomplish another object of the present invention, there is provided a chemically amplified photoresist composition including one or more photosensitive polymers each having an average-weight molecular weight of 3,000 to 100,000, and selected from the group consisting of first through sixth photosensitive polymers, and a photoacid generator contained in an amount of 1 to 15% by weight based on the total weight of the one or more photosensitive polymers.
The chemically amplified photoresist composition may further include 1 to 50% by weight of a dissolution inhibitor based on the total weight of the one or more photosensitive polymers. Also, the chemically amplified photoresist composition may further include 0.01 to 2.0% by weight of an organic base based on the total weight of the photosensitive polymer.
The photosensitive polymer according to the present invention has a cyclic backbone, and a hydroxy group is bonded to the backbone. Thus, the etching resistance of the photoresist composition containing the same is large and an adhesion to an underlying film is excellent. In particular, in the case where a secondary alcohol group is bonded to the backbone, the polymer is chemically stable so that it can be stored for a long period of time.
A photosensitive polymer and a chemically amplified photoresist composition containing the same according to the present invention will now be described. Also, a preferred photolithography process using the chemically amplified photoresist composition will be described. This invention may, however, be embodied in many different forms, and these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
A photosensitive polymer according to a first embodiment of the present invention includes a first monomer which is norbornene ester having C1 to C12 aliphatic alcohol as a substituent and a second monomer which is maleic anhydride. In order to increase the stability of the photosensitive polymer, the C1 to C12 aliphatic alcohol is preferably secondary alcohol.
The photosensitive polymer according to a first embodiment of the present invention is represented by the formula (1): 
wherein R1 is an oxycarbonyl having C1 to C12 aliphatic alcohol as a substituent and the weight average molecular weight of the polymer is in the range of 3,000to 100,000.
Preferably, the C1 to C12 aliphatic alcohol is secondary alcohol. For example, 2xc2x0 propanol can be used as the C1 to C12 aliphatic alcohol.
The photosensitive polymer has a cyclic backbone, and a hydroxy group is bonded to the backbone. Thus, the etching resistance of the photoresist composition containing the same is large and an adhesion to an underlying film is excellent. In particular, in the case where a secondary alcohol group is bonded to the backbone, the polymer is chemically stable so that it has excellent durability.
A photosensitive polymer according to a second embodiment of the present invention includes, in addition to the first monomer and the second monomer of the first embodiment, at least one third monomer selected from the group consisting of norbornene carboxylic acid, norbornene ester having a C6 to C20 alicyclic ester having C as a substituent, norbornene ester having an acid-labile group as a substituent, (meth)acrylic acid, (meth)acrylate having C6 to C20 aliphatic alcohol as a substituent, acid-labile group pendent to the (meth)acrylate, and (meth)acrylate having a C6 to C20 alicyclic hydrocarbon as a substituent.
Like in the first embodiment, the C1 to C12 aliphatic alcohol is preferably secondary alcohol.
The C6 to C20 alicyclic hydrocarbon group is preferably adamantyl, norbornyl, isobornyl or naphtyl, the acid-labile group pendent to the norbornene ester is preferably t-butyl, 1-alkoxy ethyl or tetrahydropyranyl, the (meth)acrylate having C1 to C12 aliphatic alcohol as a substituent is preferably 2-hydroxyethyl, and the acid- labile group pendent to the (meth)acrylate is preferably t-butyl or 2-methyladamantyl.
In particular, a suitable first monomer includes 2xc2x0 propanol norbornene ester, and a suitable third monomer includes adamantyl (meth)acrylate, norbornyl (meth)acrylate, isobornyl (meth)acrylate, naphtyl (meth)acrylate, t-butyl (meth)acrylate or 2-methyladamantyl (meth)acrylate.
The photosensitive polymer according to a third embodiment of the present invention includes a first monomer selected from the group consisting of norbornene having aliphatic alcohol as a substituent, norbornene carboxylic acid, norbornene having a C1 to C12 aliphatic hydrocarbon group with a carboxy group pendent thereto as a substituent; and norbornene having a C1 to C12 aliphatic hydrocarbon group with a carboxylic anhydride group pendent thereto as a substituent; a second monomer which is maleic anhydride; and a third monomer selected from the group consisting of norbornene ester having a C6 to C20 alicyclic hydrocarbon group as a substituent and(meth)acrylate having a C6 to C20 alicyclic hydrocarbon group as a substituent, and the weight average molecular weight of the monomers is in the range of 3,000 to 100,000.
If the C6 to C20 alicyclic hydrocarbon group is bonded to the backbone of the polymer, the unexposed photosensitive polymer is not easily dissolved in a developing solution. Thus, in the case where a photoresist layer is made of such a photosensitive polymer, since the photoresist layer of the unexposed region is not easily dissolved in a developing solution, a loss in the thickness of a photoresist pattern (TPR loss), which is encountered in the conventional art, can be suppressed.
In particular, a suitable third monomer includes adamantyl (meth)acrylate, norbornyl (meth)acrylate, isobornyl (meth)acrylate and naphtyl (meth)acrylate.
The photosensitive polymer according to a fourth embodiment of the present invention includes a first monomer which is norbornene ester having C1 to C12 aliphatic alcohol as a substituent; a second monomer which is maleic anhydride; a third monomer selected from the group consisting of norbornene carboxylic acid, norbornene ester having a C6 to C20 alicyclic hydrocarbon group as a substituent and acid-labile group pendent to the norbornene ester; and, a fourth monomer selected from the group consisting of (meth)acrylic acid, (meth)acrylate having C1 to C12 aliphatic alcohol as a substituent, (meth)acrylate having an acid-labile group as a substituent, and (meth)acrylate having a C6 to C20 alicyclic hydrocarbon group as a substituent, and the weight average molecular weight of the polymer is in the range of 3,000 to 100,000.
Preferably, a suitable first monomer includes 2xc2x0 propanol norbornene ester, a suitable third monomer includes t-butyl norbornene ester, and a suitable fourth monomer includes adamantyl (meth)acrylate, norbornyl (meth)acrylate, isobornyl (meth)acrylate, naphtyl (meth)acrylate, t-butyl (meth)acrylate or 2-methyladamantyl (meth)acrylate.
The photosensitive polymer according to a fifth embodiment of the present invention includes a first monomer selected from the group consisting of norbornene having C1 to C12 aliphatic alcohol as a substituent, norbornene carboxylic acid, norbornene having a C1 to C12 aliphatic hydrocarbon group with a carboxyl group pendent thereto as a substituent, and norbornene having a C1 to C12 aliphatic hydrocarbon group with a carboxylic anhydride pendent thereto as a substituent; a second monomer which is maleic anhydride; a third monomer selected from the group consisting of norbornene carboxylic acid, norbornene ester having a C6 to C20 alicyclic hydrocarbon group as a substituent, and norbornene ester having an acid-labile group as a substituent; and a fourth monomer which is (meth)acrylate having a C6 to C20 alicyclic hydrocarbon group as a substituent, and the weight average molecular weight of the polymer is in the range of 3,000 to 100,000.
Preferably, a suitable first monomer includes norbornene methanol, and a suitable third monomer includes t-butyl norbornene ester, suitable fourth monomer includes adamantyl (meth)acrylate, norbornyl (meth)acrylate, isobornyl (meth)acrylate or naphtyl (meth)acrylate.
The photosensitive polymer according to a sixth embodiment of the present invention includes a first monomer which is norbornene having C1 to C12 aliphatic alcohol as a substituent, norbornene carboxylic acid, norbornene having a C1 to C12 aliphatic hydrocarbon group with a carboxylic group pendent thereto as a substituent, norbornene having a C1 to C12 aliphatic hydrocarbon group with a carboxylic anhydride group pendent thereto as a substituent, or norbornene ester having C1 to C12 aliphatic alcohol as a substituent; a second monomer which is maleic anhydride; a third monomer which is norbornene ester having an acid-labile group as a substituent; and a fourth monomer which is norbornene ester having a C6 to C20 alicyclic hydrocarbon group as a substituent, and the weight average molecular weight of the polymer is in the range of 3,000 to 100,000.
Preferably, a suitable first monomer includes 2xc2x0 propanol norbornene ester, a suitable third monomer includes t-butyl norbornene ester, and a suitable fourth monomer includes adamantyl norbornene ester, norbornyl norbornene ester, isobornyl norbornene ester or naphtyl norbornene ester.
The photosensitive polymers according to the first through sixth embodiments of the present invention can be represented by the formula (2): 
wherein R1 is a carboxy group, a C1 to C12 aliphatic alcohol group, a C1 to C12 aliphatic hydrocarbon group having a carboxy group pendent thereto as a substituent, a C1 to C12 aliphatic hydrocarbon group having a carboxylic anhydride group pendent thereto as a substituent or a C1 to C12 aliphatic alcohol oxycarbonyl; R2 is hydrogen, a C6 to C20 alicyclic hydrocarbon group or an acid-labile group; R3 is hydrogen or methyl; R4 is hydrogen, a C1 to C12 aliphatic alcohol, an acid-labile group or a C6 to C20 alicyclic hydrocarbon group; l, m, n, and p are integers, where l/(l+m+n+p) equals 0.05 to 0.5, m/(l+m+n+p) equals 0.3 to 0.5, n/(l+m+n+p) equals 0.0 to 0.3, p/(l+m+n+p) equals to 0.0 to 0.4; and the weight average molecular weight of the polymers is preferably in the range of 3,000 to 100,000.
As described in the first through sixth embodiments, R1 is preferably a hydroxymethyl group or a C1 to C12 aliphatic alcohol oxycarbonyl group to improve adhesion to an underlying film. In particular, the C1 to C12 aliphatic alcohol is secondary alcohol, preferably 2xc2x0 hydroxypropyloxycarbonyl, to improve the stability of the polymer.
Also, R2 or R4 is preferably a C6 to C20 alicyclic hydrocarbon group so that the photoresist layer of an unexposed region may not be easily dissolved in a developing solution.
Usable C6 to C20 alicyclic hydrocarbon groups include adamantyl, norbornyl, isobornyl or naphtyl.
Also, a monomer in which R2 is an acid-labile group such as t-butyl and a monomer in which R2 is a C6 to C20 alicyclic hydrocarbon group may be simultaneously used to further increase the etching resistance.
In order to increase a difference in the solubility of the photosensitive polymer for a developing solution before and after exposure, that is, contrast, at least one of R2 and R4 is preferably an acid-labile group. In R2, examples of the acid-labile group include t-butyl, 1-alkoxyethyl or tetrahydropyranyl, and in R4, examples of the acid-labile group include t-butyl or 2-methyladamantyl.
Since the backbone of the photosensitive polymer according to the present invention has a cyclic structure, the etching resistance thereof is large. In the case where a hydroxy group is bonded to the backbone, the polymer exhibits good adhesion to underlying layers and high wettability to a developing solution. Also, in the case where the alicyclic hydrocarbon group is bonded to the backbone, the etching resistance is further increased and the solubility of the photoresist layer of an unexposed region to the developing solution is reduced. Thus, it is possible to prevent the thickness of a photoresist pattern from decreasing.
A chemically amplified photoresist composition of the present invention includes the above-described photosensitive polymer and a photoacid generator. The photoacid generator is preferably contained in an amount of 1 to 15% by weight based on the total weight of the photosensitive polymer. The photoacid generator is preferably a substance that has high thermal stability. Therefore, suitable photoacid generators include triarylsulfonium salts, diaryliodonium salts, sulfonates or N-hydroxysuccinimide triflates. Examples of triarylsulfonium salts include triphenylsulfonium triflate and triphenylsulfonium antimonate. Examples of diaryliodonium salts include diphenyliodonium triflate, diphenyliodonium antimonate, methoxydiphenyliodonium triflate and di-t-butyldiphenyliodonium triflate. Examples of sulfonates include 2,6-dinitro benzyl sulfonate and pyrogallol tris(alkyl-sulfonates).
Preferably, the photoresist composition of the present invention further includes 0.01 to 2.0% by weight of organic base based on the total weight of the photosensitive polymer. Suitable organic bases include triethylamine, triisobutylamine, triisooctylamine, diethanolamine or triethanolamine. The organic base is added for preventing a pattern from being deformed due to acidolysis of photoresist composition forming unexposed regions after exposure, which results from diffusion of the acid generated at the exposed regions into the unexposed regions.
Also, the photoresist composition according to the present invention preferably further includes 1 to 50% by weight of a dissolution inhibitor based on the weight of the photosensitive polymer. A material which has an acid-labile group is used as the dissolution inhibitor such that the dissolution inhibitor in the exposed region is easily dissolved in a developing solution.
In the case where the composition contains a dissolution inhibitor, an acid-labile group is not necessarily contained in the photosensitive polymer. In the case where the composition contains a photosensitive polymer having the acid-labile group pendent thereto and a dissolution inhibitor, a difference in the solubility between an exposed region and an unexposed region is noticeably increased, thereby improving the contrast. Examples of the dissolution inhibitor include t-butyl lithocholate.
1. Synthesis of Norbornene ester Having C1 to C12 aliphatic alcohol as a Substituent
Cyclopentadiene (I) is dissolved in an organic solvent and then C1 to C12 aliphatic alcohol substituted acrylate (II) is added thereto to prepare norbornene ester (III) as expressed in the following reaction scheme (1): 
wherein R0 is C1 to C12 aliphatic alcohol.
2. Synthesis of norbornene Having C1 to C12 aliphatic alcohol as a Substituent
5-norbornene-2-aldehyde (V) is dissolved in aliphatic alcohol magnesium bromide (IV) solution to prepare norbornene having C1 to C12 aliphatic alcohol as a substituent (VI) by a substitution reaction, as expressed in the following reaction scheme (2): 
wherein R0 is an aliphatic hydrocarbon and y is an integer from 1 to 10.
3. Synthesis of norbornene ester Having C6 to C20 alicyclic hydrocarbon or an acid-labile group as a substituent
Cyclopentadiene is dissolved in an organic solvent and then acrylate having C6 to C20 alicyclic hydrocarbon as a substituent or acrylate having an acid-labile group as a substituent is added thereto to prepare norbornene ester.
A first monomer (VII) synthesized in the first or second method, a second monomer (VIII), a third monomer (IX) synthesized by the third method, and a fourth monomer (X) are dissolved in an organic solvent, for example, toluene, in a mixture ratio of l:m:n:p, and then a polymerization initiator, for example, azobisisobutyronitrile (AIBN) is added to carry out polymerization, thereby preparing a polymer, as expressed in the following reaction scheme (3): 
wherein, in the case where n and p are each zero, l and m are equal to each other, and R1 is a C1 to C12 aliphatic alcohol oxycarbonyl group, and a polymer represented by the formula (1) is prepared.
The chemically amplified photoresist composition according to the present invention is prepared by dissolving the photosensitive polymer prepared in the above-described manner and a photoacid generator in an appropriate solvent and mixing the same. Here, the photoacid generator is mixed in an amount of 1 to 15% by weight based on the weight of the polymer. Also, it is preferable to complete the photoresist composition by further dissolving 0.01 to 2.0% by weight of an organic base based on the weight of the polymer.
The chemically amplified photoresist composition prepared in the above-described manner can be used for a general photolithography process, and is particularly suitable for forming a fine pattern to satisfy a design rule of 0.20 xcexcm or smaller when using an ArF excimer laser as an exposure light source.
First, the photoresist composition is coated on a substrate where a patterning object material layer is formed to form a photoresist layer having a predetermined thickness, preferably 0.2 to 2 xcexcm. Since the photoresist composition according to the present invention comprise a hydroxy group, it can be easily coated on the substrate. Subsequently, pre-baking is carried out on the photoresist layer. The pre-baking step is performed at a temperature of 70 to 160xc2x0 C. for 30 to 360 seconds. After the pre-baking step, the photoresist layer is exposed using a mask having a predetermined pattern, using an exposure light source having a wavelength of 248 nm or less, preferably an ArF excimer laser having a wavelength of 193 nm. Acid is generated from the photoacid generator contained in the photoresist layer by exposure. The photosensitive polymer is acidolyzed by the catalytic action of the thus-generated acid to form a lot of carboxy groups, as expressed in reaction scheme 4. As a result, a large amount of hydrophilic groups, e.g., carboxy groups, are produced in the exposed region of the photoresist layer. Thus, a noticeable difference in the polarity of the photoresist layer is created between an exposed region and an unexposed region. That is to say, contrast is noticeably increased. 
The parentheses represent that R2 and R4 are not acidolyzed, but are retained after exposure in the case where they are C6 to C20 alicyclic hydrocarbons.
After exposure, the photoresist layer is thermally treated for a short time before development, which is referred to as a post-exposure-thermal treatment. The post-exposure-thermal treatment is performed for the purpose of activating acidolysis by the acidic catalyst, that is, for the purpose of increasing contrast by further activating acidolysis of exposed regions by the acidic catalyst to acidolyze ester contained in the photosensitive polymer into carboxy groups.
Next, development is performed using an appropriate developing solution to complete a photoresist pattern. Here, the developing solution used is a developing solution for general development processes, for example, 2.38% by weight of tetramethylammonium hydroxide (TMAH). In the case where a C6 to C20 alicyclic hydrocarbon is bonded to the backbone of the photosensitive polymer constituting the photoresist layer, since the photoresist layer in the unexposed region is not easily dissolved in the developing solution, the thickness of the photoresist layer in the unexposed region is not reduced, unlike the conventional art.
After forming the photoresist pattern, a patterning object layer is etched to form a desired pattern. The photoresist pattern of the present invention is formed of a photoresist layer including a photosensitive polymer having a cyclic backbone and a tertiary alicyclic hydrocarbon bonded as a substituent, and thus the etching resistance thereof is large. Therefore, a pattern having a good profile, that is, having a precise critical dimension, can be formed.